Procedures exist for replacing diseased intervertebral disks in which the disk material is typically removed from between adjacent vertebral bodies, and the adjacent bodies are fused. This has been done with a cage placed in between the bodies to fix them to each other, generally to support and promote fusion between the adjacent vertebrae.
U.S. Pat. No. 6,102,950, for example, discloses an intervertebral fusion device. A wedge body is nested within a cage component. A contraction mechanism with a threaded shaft draws the wedge body into the cage component to increase the angle between upper and lower members of the cage component to achieve a proper angle of lordosis. The cage component also has a plurality of spines, each with a spike facing outwardly through passages. Ramps on the wedge deploy the spikes into the endplates of the vertebral bodies. U.S. Pat. Nos. 5,653,763 and 5,554,191 disclose cages that employ different means to expand the cages vertically.
While fusion cages provide no mobility between the fused vertebrae, other prostheses have been developed to permit motion between the adjacent vertebrae. One of these is known as the Link, sold by the Link Spine Group, Inc., has top and bottom plates that are implanted between vertebral bodies, and between which a core is placed. The plates and the core contact at rounded surfaces to allow the plates to move about the core.
These devices have a fixed width. Due to the positioning of tendons and vascular anatomy, the opening available on the anterior side of the spinal column for implanting the prosthesis is narrower than the width of the bodies, and the prosthesis are narrower as well. U.S. Pat. No. 6,395,031 shows an intervertebral spacer that is expandable laterally once implanted. The spacer has a fixed height, and several are inserted to contact the face of the vertebral bodies.
Patent Application Publication No. US 2002/009944 A1 shows a modular interbody implant with a fixed height and made from bone, and having lateral spacers that receive therebetween a connecting member. The three pieces taught as being assembled between the vertebrae.
Accordingly, there is a need for an improved disk prosthesis that can facilitate implantation by providing both axial and lateral expansion, and that provides improved support to the vertebral bodies by maximizing the surface area contact between the prosthesis and adjacent vertebrae, and by supporting the vertebrae at the portion where the bone is strongest.